To realize high information society and multimedia, processing of large volume information at very high speed is required, and for that purpose, optical processing technology which replaces conventional electronic processing is inevitable. To realize the optical processing technology, development of nonlinear optical elements such as wavelength conversion elements, supercontinuous white light generating elements and optical switching elements is in progress.
As a glass applicable to such nonlinear optical elements, a Bi2O3—B2O3—SiO2—Al2O3—Ga2O3—CeO2 glass has been proposed. For example, this glass is disclosed in Table 1 of JP-A-2001-213640.
The glass applicable to nonlinear optical elements is required to be an optical glass having a high third order nonlinear coefficient, and in order that the glass has a high third order nonlinear coefficient, it is effective to increase its refractive index. Further, the glass is also required to be free from lead.
A conventional glass having a refractive index n of 2.19 at a wavelength of 1,550 nm is disclosed as an example (Example 3, core) in Table 1 of JP-A-2001-213640, and the third order nonlinear coefficient of this conventional glass is considered to be relatively high.
When a nonlinear optical element is to be produced employing such a glass, it is required to prepare glass first and then to apply a heat treatment to the glass. For example, when an optical fiber is to be produced, usually a glass preform is prepared first, which is drawn while a heat treatment is applied thereto to produce an optical fiber.
However, the conventional glass has a problem in thermal stability such that it is likely to be crystallized when subjected to heat treatment.
It is an object of the present invention to provide an optical glass which solves such a problem and an optical fiber.